Reports the number of users connected via the callback service, where the device dials the user back rather than accepting the inbound call directly, for this specific office direction — an outbound trunk grouping identified by an office-direction number from 0 to 255 (the table is indexed by that number). An admin polls this counter alongside its sibling userStatisticsOdn* objects to see how the mix of dial-up service types is distributed for this particular odn (this table's own source DESCRIPTION notes the callback service is not supported on release R001); it lets an admin see session-type counts broken down by which upstream office/trunk group the calls arrived through.